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> isn't it just some form of polling at the end of the day?

Probably long-poll, a single connection from client to server kept alive with the occasional byte sent one way which sends the message and disconnects when there is something to send (the disconnect, requiring a new request from the client is because some clients won't process what has been sent immediately unless the connection is closed).

I once wrote a messaging client that operated this way. It is efficient in terms of bandwidth use and client footprint, though if you are using a process based we server it can be quite inefficient there (an event driven service on few processes/threads is far more efficient for handling many long-lived low-activity connections).

That's in keeping with how I think of it: open connection from the client with some reasonable expectations set around e.g. reconnection behavior.

Looks like Chrome and Firefox have had support for quite some time. I'm alright with that.

IE is just trying to look all hip and cool and EventSource hasn't generated much hype so it doesn't get implemented.. shame.